This invention relates to a cooling system for a four stroke internal combustion engine and more particularly to an improved liquid cooling system for such engines.
In four cycle engines and particularly those adapted for use in outboard motors, both the cylinder block and cylinder head in which the intake and exhaust ports are formed are provided with respective cooling jackets. Frequently there may be an exhaust manifold or exhaust passage formed in the cylinder block which communicates with the discharge of the exhaust ports of the cylinder heads for discharging the exhaust gases back to the atmosphere through the body of water in which the watercraft is operated. The cylinder block exhaust passage is also normally water cooled.
In connection with such engines, it has been the normal practice to circulate the cooling water first through the cylinder block around its cylinder liners and around the exhaust manifold in the cylinder block. The coolant is then delivered from the cylinder block cooling jacket to the cylinder head cooling jacket for cooling the cylinder head and the exhaust ports formed therein. This means that by the time the cooling water has reached the exhaust ports it has been quite heated. Obviously, the efficiency of the cooling system depends upon the difference in temperature between the coolant and the portion of the engine being cooled. As a result, the cooling of the exhaust gases is basically inefficient and hot spots in the cylinder head can result.
It is, therefore, a principal ob]ect of this invention to provide an improved cooling system for an internal combustion engine.
It is a further object of this invention to provide an improved cooling system for a four cycle internal combustion engine employed in an outboard motor.
It is a further object of this invention to provide an improved liquid cooling system for a four cycle engine in which the cooling of the cylinder head exhaust ports is promoted.